refactor: use negotiator and intl-localematcher to get the preferred language

Author: byron-okta

package-lock.json

@@ -6,13 +6,15 @@
         "url": "https://github.com/jsonwebtoken/jsonwebtoken.github.io"
     },
     "dependencies": {
+        "@formatjs/intl-localematcher": "^0.5.10",
         "@octokit/rest": "^18.0.12",
         "dotenv": "^8.2.0",
         "express": "^4.17.1",
         "express-sslify": "^1.2.0",
         "jstransformer-markdown": "^1.2.1",
         "jstransformer-markdown-it": "^2.1.0",
         "lodash.debounce": "^4.0.8",
+        "negotiator": "^1.0.0",
         "pug": "^2.0.4",
         "querystring": "^0.2.0"
     },
@@ -83,4 +85,4 @@
         "build:libraries": "node libraries.js"
     },
     "heroku-run-build-script": true
-}
+}

package.json

@@ -2,6 +2,8 @@ const express = require("express");
 const enforce = require("express-sslify");
 const languages = require("./libraries.json");
 const dotenv = require("dotenv").config();
+const Negotiator = require("negotiator");
+const localeMatcher = require("@formatjs/intl-localematcher");
 
 const app = express();
 
@@ -19,16 +21,17 @@ if (process.env.NODE_ENV === "production") {
 }
 
 app.use((req, res, next) => {
-    const acceptLanguage = req.headers['accept-language'];
+    const languagesFromRequestHeaders = new Negotiator(req).languages();
+    const LANGUAGE_CODES = ["en", "ja"]
+    const DEFAULT_LANGUAGE_CODE = ["en"]
 
-    if(acceptLanguage){
-        const preferredLanguage = acceptLanguage.split(",")[0].split("-")[0];
-
-        req.preferredLanguage = preferredLanguage;
-    }else{
-        req.preferredLanguage = 'en';
-    }
+    const languageFromRequestHeader = localeMatcher.match(
+        languagesFromRequestHeaders,
+        LANGUAGE_CODES,
+        DEFAULT_LANGUAGE_CODE,
+    );
 
+    req.preferredLanguage = languageFromRequestHeader;
     next();
 })